The purpose of a cooling coil drain pan is to capture condensed water from a cooling coil, and route it to a drain, without leaving areas of stagnant water behind Drain pans are a potential source of microbial contamination. Until recently, most air handlers and terminal units with cooling coils were designed with flat drain pans. However, ASHRAE Standard 62 now stipulates regarding drain pans that pans intended to collect and drain liquid water shall be sloped at least 0.125 inches per foot or shall be otherwise designed to ensure that water drains freely from the pan whether the fan is on or off.
Vertically positioned cooling coils are mounted in a vertical or near vertical position. Horizontally positioned cooling coils are mounted in a horizontal, or near horizontal position. In both cases, condensate flows downward with gravity, into the drain pan.
The prior art reveals applications of permanently installable horizontally positioned dual pass cooling coils. In U.S. Pat. No. 5,816,315 of Stark, horizontally extending cooling coils are used with plate-type cross flow air-to-air heat exchangers in a dehumidification application. In U.S. Pat. No. 5,913,360 of Stark, horizontally extending cooling coils are used in conjunction with air flow dampers in another dehumidification application.
The prior art also discloses vertical or near vertical positioned cooling coils with narrow drain pans. For example, U.S. Pat. No. 4,135,370 of Hosoda describes a dehumidification system with a vertically oriented evaporator 4 with a single drip pan 7 below the evaporator 4. U.S. Pat. No. 6,203,036 of LaVaute describes a Busing Cart with separate drip pans in general for transporting non-analogous dishes. U.S. Pat. No. 6,484,512 of Anderson describes temperature controlled drawers that use a plurality of drip pans, such as disclosed in two separate non-integral drip pans 89 and 148 below a vertically oriented heat sink 124 in FIG. 5.
Unlike vertical or near vertical positioned cooling coils, such as in Hosada '370, that require relatively narrow drain pans, horizontal, or near horizontal positioned, cooling coils, such as cooling coils 66 of Stark '315 and Stark '360, have a larger drip surface area and therefore require larger drain pans for collecting condensed moisture and routing it to drainage connection(s).
Problems with single large drain pans under horizontally extended cooling coils are that they exceed the width of traditional construction materials and therefore require seams in the drain pan floor to join pieces together. This joining results in potential for leaks, added assembly labor, uneven and non-uniform pan surfaces which thereby increases the required slope to ensure full drainage with no areas of stagnant water.                a. Seams in the pan floor increase the possibility of leaks, increase cost of manufacturing and, in the case of stainless steel; heat from welding changes the properties of the metal at the weld joint, causing rust and accelerated deterioration. Welding long seams of a drain pan material is known to cause “buckling” which leads to pockets of trapped stagnant condensate. The remedy using single large drain pans is to increase the height dimension, to ensure complete drainage.        b. Increased slope means the pan height dimension must increase and consequently, the height of the entire apparatus must increase to ensure full drainage to the low point or drainage connection(s). Without proper slope, areas of stagnant water form on the surface of large pans. These areas of stagnant water are caused by a non-uniform surface that is a natural tendency over large surfaces. Thick material and/or stiffeners are needed to ensure a uniform flat and adequately sloped surface.        c. Therefore, there is a need to provide efficient drainage of water underneath horizontally extending cooling coils.        